Electron-beam cured varnishes enjoy considerable advantages over other varnishing systems from an environmental as well as strength point of view. The possibilities of obtaining a completely cured varnish layer and to be able to use larger amounts of varnish per m.sup.2 produce application conditions that surpass those offered by traditional varnishing systems.
Electron-beam curing equipment is expensive, for which reason it is used only in fields of application wherein considerable advantages stand to be gained from using electron-beam cured varnishes. Since abrasion resistance is a quality that is of greater importance in flooring materials than in any other constructional material and since in addition flooring material is a bulk product, it is a natural field of application for this technology.
In the Swedish Patent Specification 501 526 is described a method of mechanically texturing a smooth and laminated/foiled surface by means of electron-beam cured varnish. This method has proved to provide considerable productivity gains compared with other texturing techniques, particularly in the production of boards to be further treated into flooring boards.
In the production in accordance with this method lamination equipment is available wherein a paper foil is applied against a board by means of a thermoplastic glue. The material is submitted to high temperatures in order to produce rapid curing. When the completely varnished laminated boards leave the production line they have a temperature around 40.degree. C. when stacked. The boards must then be cooled for a duration of at least 48 h before the subsequent treatments may be initiated. Treatment of the material before the lapse of this period increases the risk of the flooring boards warping later on. The reason therefor is uneven temperatures in the material during the treatment. This is a well-known problem known to all manufacturers of thin flooring boards formed with melamine surfaces of various kinds. In the respective production processes associated with this kind of material even larger amounts of heat than those mentioned above are supplied.
Although this problem may be restricted by using new types of glue reacting at lower temperatures, the solution is nonetheless insufficient to satisfactorily solve the problem.
From the exploitation of this prior-art method e.g. the following further experience has been gained, viz.:
Only completely pre-impregnated paper foils may be used to avoid air bubbles in the varnished surface. PA1 The magnitude of the investment makes the productivity factor particularly important. PA1 The speed (and thus the productivity) of the board production line is determined by the lamination technique, the varnish application technique, and the texturing technique used. The sandwich constructions produced today as a surface layer (board, glue, foil, varnish) may exhibit weakness at the edges of the finish flooring boards, unless amounts of varnish of at least 130 g/m2 are used. PA1 The quality of the pre-impregnated decorative foil is of essential importance to the structure as a whole. PA1 In reality, amounts of varnish of 70-80 g/m.sup.2 are sufficient to obtain adequate strength in flooring boards for use in houses.